Dissertations / Theses on the topic 'Atom-optics'
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Pax, Paul Henry 1958. "Few-atom effects in atom optics." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/288794.
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Despite the many advances and achievements in the fields of atom optics and atom cooling, there remains a wealth of dynamical detail to be filled in. While the main features of the important phenomena of atomic cooling, trapping and manipulation by electromagnetic fields are well understood, there are interesting subsidiary effects that are worth our attention. An example, which we discuss in Ch. 5 is the discovery that atomic diffusion in optical lattices may not follow the normal diffusion equation. The work reported in this dissertation represents an investigation into possible few-body effects in some atom optical configurations of interest. The effects of indistinguishability, through the exchange force, on atomic diffraction by standing wave light fields is considered in Ch. 2. In Ch. 3, after a brief overview of atomic collisions in light fields, we look at the role that the dipole-dipole interaction might play, again in atomic diffraction. Chapters 4 and 5 are concerned with optical lattices, and lay the ground work for a study of the effect of the dipole-dipole interaction on the dynamics of atoms confined in such lattices.
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Goldstein, Elena Vladimirovna 1962. "Nonlinear atom optics." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/289255.
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In contrast to electromagnetic fields, matter-wave fields are intrinsically interacting due to the presence of atom-atom collisions. Hence, matter-wave optics becomes effectively nonlinear as soon as the atomic densities are high enough that collisions can no longer be ignored. The goal of this dissertation is to study selected aspects of atom optics under such conditions. Specifically, Chapter 2 studies the near-resonant dipole-dipole interaction between two atoms in tailored vacua. In contrast to spontaneous emission, whose rate is known to be influenced by the type of vacuum the atom interacts with, we find that the dipole-dipole potential is determined only by the free space vacuum and is not modified either by thermal or squeezed vacua. In addition in the far off-resonance regime we find that the squeezed vacuum results in an additional contribution to the effective potential governing the evolution of the atomic ground state. In the second part of the dissertation, which comprises Chapter 3, we then study several aspects of the many-body theory of atomic ultracold systems in situations where the nonlinearity arises due to the two-body dipole-dipole interaction. After a formal theoretical development we discuss the possibility of using atomic phase conjugation off Bose condensates as a diagnostic tool to access the spatial coherence properties and to measure the lifetime of the condensate. We argue that phase conjugation provides an attractive alternative to the optical methods of probing condensate proposed in the past. We further study the elementary excitations in a multicomponent Bose condensates and determine the quasi-particle frequency spectrum. We show that in that case interferences resulting from cross-coupling between the condensate components can lead to a reversal of the sign of the effective two-body interaction and to the onset of spatial instabilities.
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Vernier, Aline. "Phase dependent atom optics." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2560/.
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Quantum interference in atomic media has elicited interest for a very wide range of investigations and applications. As well as being a fascinating effect in itself, it also found applications in spectroscopy, nonlinear optics and has recently been drawing attention in the field of quantum optics for the realisation of sources of entangled photons, optical switching, and quantum information storage. The work presented in this thesis consists of two main projects centred around the theme of quantum interference in atomic processes. As cooled atomic vapours provide favourable conditions for the investigation of coherent phenomena, a magneto-optical trap was built for the future study of quantum interference in four-level link- ages. The number of trapped atoms is estimated to be ≈ 8 × 10^8, and the density to be ≈ 10^9 atoms per cubic centimetre. This represents the first stage of an ongoing study of quantum interference in four-level linkages. However, coherent effects can also be observed in hot vapours. A spontaneous, highly efficient, frequency up-conversion arising from four-wave mixing can indeed be observed in Rubidium. This complex phenomenon was investigated experimentally and theoretically so as to improve the conversion efficiency, and understand the underlying physics. The optimum conditions found in this study yield 1 mW of converted light for 40 mW of pumping light. As part of the study of the phase coherence of the process, the conversion of spatial modes in the four-wave mixing process was also examined. The observation of the transfer of orbital angular momentum in the process is reported, and a preliminary theoretical interpretation is presented.
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Taylor, Byron Brooks 1965. "Topics in atom optics." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/289433.
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This dissertation covers the field of atom optics and is divided into four main chapters: In Chapter 2 we investigate the effects of light forces on the center-of-mass motion of two-level atoms. This will lead to the discussion of two regimes: the "ray optic" and the "wave optic" regime. In the first case, an atom is well localized in the field which allows a comparison to be made with classical ray optics. In the second case, the atom is strongly delocalized which leads to a wave treatment and allows a comparison with diffractive optics. We finish this chapter with an example in each regime: Doppler cooling for ray optics and an atomic Fabry-Perot for wave optics. In Chapter 3 we extend the results of the previous chapter to the diffraction of atoms by a standing light field. We cover three regimes in the near resonant Kapitza-Dirac effect: the Raman-Nath, the Bragg and the optical Stern-Gerlach regime. In the Raman-Nath and Bragg regimes, the wave-packet is strongly delocalized compared to the period of the standing wave. In contrast, the Stern-Gerlach regime has a small spatial extent. The Raman-Nath and Bragg regimes are differentiated in their treatment of the kinetic energy. Initially we only discuss coherent interactions. In the later half of this chapter we introduce spontaneous emission and show how its presence affects the diffraction pattern in each of these regimes. In Chapter 4 we cover various atomic cooling schemes: strong field Sisyphus cooling, adiabatic cooling, evaporative cooling, polarization gradient cooling and velocity selective coherent population trapping. We begin with a brief discussion of atomic temperature. We then cover two cooling schemes for two-level atoms. We eventually move to multi-level atoms and end this chapter with a two-atom multi-level system. In Chapter 5 we conclude with a brief discussion of practical uses and devices that may arise from atom optics such as lenses, mirrors, gravitational interferometry, lithography and atomic clocks.
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D'Arcy, Michael Brendan. "Quantum chaos in atom optics." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249527.
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Holst, B. "Atom optics and surface growth studies using helium atom scattering." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604194.
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The first part of thesis investigates the application of electrostatically deformed single crystal membranes as focusing elements for a neutral atomic beam in an ultra high resolution diffractometer. The second part demonstrates the versatility of helium as a surface science tool in a study of the growth of ultra thin Cu-films on Pt(111). Chapter 1 gives an introduction to the subject of atom focusing with an overview of the various methods hitherto applied. Chapter 2 presents a theoretical framework for the application of a focusing element in an ultra high resolution diffractometer. An off axis reflected ray equation is derived from which aberration coefficients are obtained and used to determine the best obtainable performance. Chapter 3 presents equations for calculating deformation of radically symmetric thin plates (membranes). Furthermore interferometry experiments are presented which investigate the deformation of single crystal Au(100) and Si(100) in varying fields. The films mechanical properties are discussed, and contourmaps obtained from the interferometry experiments used in computer simulations to evaluate their focusing properties. Chapter 4 contains the experimental methods and sample preparation of the two types of samples used here. The Pt(111) and the Si(111)-H(1 x 1) eventually chosen for the mirror. In particular a new mount specially designed for the focusing mirror is described in detail.
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Oskay, Windell Haven. "Atom optics experiments in quantum chaos." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3040634.
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Perreault, John D. "Using Atom Optics to Measure van der Waals Atom-Surface Interactions." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1317%5F1%5Fm.pdf&type=application/pdf.
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Rosenbusch, Peter. "Atom optics with an adaptable magnetic reflector." Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341516.
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Chu, Yiwen. "Quantum optics with atom-like systems in diamond." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11310.
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The nitrogen vacancy (NV) center in diamond is a unique quantum system that combines solid state spin qubits with coherent optical transitions. The spin states of the NV center can be initialized, read out, and controlled with RF fields at room temperature. It can be coupled to other spin systems in the environment while at the same time maintaining an extraordinary degree of quantum coherence. Experiments utilizing the NV center's spin states have led to a wide range of demonstrations from quantum error correction to high-sensitivity magnetometry. This thesis, however, focuses on creating an interface between NV centers and light in the visible domain by making use of its optical transitions. Such an interface connects the quantum system consisting of NV centers and nuclear spins to photons, which can then be used to both manipulate the spin qubits themselves or transport quantum information over large distances.Physics
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Smyth, William Samuel. "Non-classical atom field interactions in quantum optics." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318736.
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Helsby, Stephen John. "The integration of fibre optics for atom chips." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/63326/.
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This thesis reports on the progress made towards the integration of fibre optics components for the atom chip, a device developed to manipulate matter on the atomic scale for the purpose of quantum information processing, novel applications, and fundamental research. Following in the direction of the electronics industry, miniaturisation has resulted in exquisite control of cold atoms above surfaces, allowing the vision of a matter wave toolbox to come closer to fruition. However, although the size of the components necessary for guiding atoms via magnetic or electrostatic fields has been greatly reduced, there is still a need to scale down the optical components. The development of these cavities is detailed in this thesis, from early use of evaporated gold coated mirrors to the fully integral solution of photorefractive Bragg gratings. In addition to a thorough analysis of the optical properties of these fibre gap cavities, experimental results indicate that these gap cavity devices can be constructed with the sensitivity necessary for single atom detection.
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MacCormick, Calum. "Coherent atom optics with a dilute Bose-Einstein condensate." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289230.
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Dinkelaker, Aline. "Smooth inductively coupled ring trap for cold atom optics." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=19200.
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The main topic in this thesis is the proof-of-principle experiment for an inductively coupled magnetic ring trap for applications in atom interferometry and quantum gas investigations. Atom interferometry utilises the wave nature of atoms for precision measurements of gravitational and inertial effects and to test fundamental physics. Due to their symmetry, their periodic boundary conditions and their large enclosed areas, ring traps provide attractive geometries for atom interferometry. By tightening the trap and reducing the trap radius, toroidal traps also have excellent conditions to study super uid properties in degenerate gases. The trapping potential for the inductively coupled magnetic ring trap is formed by the superposition of an external AC eld and a local AC eld, created by the induced current in a copper ring. These fields cancel in a ring and create a time-averaged trapping potential. By inducing the current in the conductor and using AC over DC elds several problems of existing trapping mechanisms are addressed. We create a smooth, scalable trapping potential for cold atoms. We load the inductively coupled ring trap with ~ 10p6s laser cooled p87sRb atoms. The atoms can be observed evolving around the ring in the horizontal plane, until the ring is completely filllled. We record vacuum limited lifetimes of ~ 1:3s after initial Majorana losses. With an added o set eld we also gain exibility in the trap geometry regarding the radius (~5 mm) and the trap width (~0:5 mm). In a subsequent experiment, the setup and the ring trap parameters are changed to allow for the creation of p87sRb Bose-Einstein condensate and for the implementation of atom interferometry in the ring trap. A vertical, smaller ring trap with a radius of ~ 1:8 mm is created. Laser cooled atoms are loaded either at the top or at the bottom of the ring.
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Ayachitula, Rajani. "Atom Optics Using an Optical Waveguide-Based Evanescent Field." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1276669685.
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Lonij, Vincent P. A. "ATOM OPTICS, CORE ELECTRONS, AND THE VAN DER WAALS POTENTIAL." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145119.
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This dissertation describes new measurements of the van der Waals (vdW) potential energy for atoms near a surface. The measurements presented here were accomplished by studying diffraction a beam of atoms transmitted through a nanograting. I will describe how we improved precision by a factor of 10 over previous diffraction measurements by studying how different types of atoms interact with the same surface. As a result of this new precision, we were able to show for the first time the contribution of atomic core electrons to the atom-surface potential, and experimentally test different atomic structure calculation methods.In addition, this dissertation will describe how changing the width of the grating bars to achieve a particular "magic" grating bar width or rotating a grating to a particular "magic" angle allows us to determine both the atom-surface potential strength and the geometry of the grating. This represents an improvement over several recent studies where uncertainties in the nanograting geometry limited precision in the measurements of the vdW potential.For a complementary measurement, also discussed in this dissertation, we collaborated with the Vigue group in Toulouse, France. In this collaboration we used an atom interferometer to measure the phase shift due to transmission through a nanograting. By combining diffraction data from Tucson with interferometry data from Toulouse we improved the precision of interferometry measurements of the atom-surface potential of a single atomic species by almost a factor of 10 over previous interferometric measurements of the vdW potential. These interferometry measurements also serve to measure the shape of the vdW potential and set a limit on non-Newtonian gravitational interactions at 1-2 nm length scales.Finally, this dissertation will discuss how nanogratings with optimized geometry can improve atom interferometers, for example, with blazed gratings. We discuss next generation atom-surface potential measurements and examine new ways of analyzing diffraction data.
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Adnan, Muhammad. "Experimental platform towards in-fibre atom optics and laser cooling." Thesis, Limoges, 2017. http://www.theses.fr/2017LIMO0109/document.
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Cette thèse décrit la conception et la réalisation d'une plateforme expérimentale pour le refroidissement par laser et le guidage d’atomes de Rb dans les fibres à cristal photonique à cœur creux (HC-PCF). Cette plateforme a pour but de fournir un système polyvalent pour explorer le refroidissement par laser à l’intérieur des fibres avec l'objectif à plus long terme de réaliser une fibre optique constituée d’un cœur rempli d’atomes froids (micro-cellule photonique). La plateforme a été conçue pour héberger plusieurs expériences sur le guidage d'atomes froids et thermiques ainsi que la spectroscopie dans les HC-PCFs pour répondre à plusieurs questions ouvertes liées par exemple à l'effet de la surface interne des HC-PCFs sur la structure énergétique des atomes ainsi que le piégeage et le refroidissement des atomes. La plateforme comprend une chambre spécifique à vide ultra-élevée (UHV) et un ensemble de lasers pour le refroidissement et le guidage des atomes à l'intérieur du HC-PCF hautement adapté. La chambre UHV a été conçue pour accueillir plusieurs HC-PCFs et deux pièges magnéto-optiques (MOT). Les HC-PCFs ont été conçus et fabriqués avec différents diamètres de cœur, contenu modal et post-traités avec des matériaux différents pour la surface interne du cœur. Par exemple, les diamètres du cœur varient de ~ 30 μm à ~ 80 μm traités avec une couche d'aluminosilicate ou une couche de PDMS afin de fournir un grand espace de paramètres pour évaluer l'effet de la surface sur les atomes confinés dans les fibres. Ainsi, le système a été construit et caractérisé. Le laser de refroidissement/repompage a été stabilisé en fréquence, avec une variance d'Allan de σ(τ)=3,8×10^(-11)/√τ. Avec ce système nous avons généré un MOT avec les deux isotopes du Rb, avec une température de refroidissement faible de l’ordre de 7 μK. La plateforme est maintenant opérationnelle pour entreprendre le premier guidage atomique et explorer la faisabilité du refroidissement des atomes à l'intérieur des HC-PCFsThis thesis reports on the design and fabrication of an experimental platform for in-fibre laser cooling of Rb and atom optics. By in-fibre laser cooling, we mean the long term aim of laser cooling thermal Rb atoms of a Photonic MicroCell (PMC), and subsequently developing what would be cold-atom photonic crystal fibre (PCF). The platform was designed to harbor several experiments on cold and thermal atom guidance and in-fibre spectroscopy so to address several open questions related for example to the effect of the core inner-wall surface on the atom energy structure and on selective fibre mode excitation for atom trapping and cooling. The completed platform comprises a specific and large ultra-high vacuum (UHV) chamber and a set of lasers for both atom cooling and atom guiding inside highly tailored hollow-core PCF (HC-PCF). The UHV chamber was designed to accommodate several HC-PCFs and two magneto-optical traps (MOT). The HC-PCF were designed, fabricated and post-processed to exhibit different core diameter, modal content and core inner surface material. For example, the mode field diameters range from ~30 µm to ~80 µm for the fundamental Gaussian-like core mode, and the surface materials include pure silica, a layer of Aluminosilicate or a layer of PDMS so to provide a large parameter space in assessing the effect of surface on the fibre-confined atoms. The system has been constructed and characterized. The cooling/repumping laser was frequency-stabilized, with measured Allan variance deviation of σ(τ)=3.8×10^(-11)/√τ. With the system we generated MOT with both isotopes of the Rb atom, with a cooling temperature as low as 7 µK. The platform is now operational to undertake the first atom guidance and explore the feasibility of atom cooling inside a HC-PCF
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Al-Amri, Mohammad D. "Cavity QED and atom optics in planar dielectric/metallic structures." Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421498.
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Murali, Kota 1980. "An approach to bridging atom optics and bulk spin quantum computation." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/62378.
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Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2003.Includes bibliographical references (p. 147-152).
This thesis is an exploration in quantum computation and modern physics. Atomic, molecular, and optical (AMO) physics, a centerpiece of modern physics, originated in the 1950's with the discovery of nuclear magnetic resonance (NMR), a field which has mostly been left behind in physics. However, NMR has recently taken yet another leap: quantum computers of up to seven qubits in size, the largest realized to-date, have been implemented by applying NMR to molecules in liquid solution. What new lessons can AMO physics learn from these advances made by NMR into quantum computation? And what can NMR quantum computation learn from the many advances made in recent AMO physics? In this work, I study two specific answers to these twin questions: the use of atom-like quantum systems beyond spin-1/2 for NMR quantum computation, and the demonstration of a modern quantum-optical phenomenon, electromagnetically induced transparency, using NMR quantum computation. Both examples build on theoretical analysis, and include experimental results, showing how atomic physics could be very useful for implementing certain quantum operations and vice versa. These investigations form the basis for an atomic physics test-bed in NMR quantum computation.
by Kota Murali.
S.M.
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Trubko, Raisa, and Raisa Trubko. "Tune-out Wavelength Measurement and Gyroscope Using Dispersion Compensation in an Atom Interferometer." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625677.
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This Dissertation describes how I used a three nanograting Mach-Zehnder atom beam interferometer to precisely measure a wavelength of light, known as a tune-out wavelength, that causes zero energy shift for an atom. I also describe how such measurements can be remarkably sensitive to rotation rates. It is well known that atom interferometry can be used to measure accelerations and rotations, but it was a surprise to find out that tune-out wavelength measurements can under certain conditions be used to report the absolute rotation rate of the laboratory with respect to an inertial frame of reference. I also describe how we created conditions which improve the accuracy of tune out wavelength measurements. These measurements are important because they serve as a benchmark test for atomic structure calculations of line strengths, oscillator strengths, and dipole matrix elements. I present a new measurement of the longest tune-out wavelength in potassium, λzero = 768.9701(4) nm. To reach sub-picometer precision, an optical cavity surrounding the atom beam paths of the interferometer was used. Although this improved the precision of our experiment by increasing the light-induced phase shifts, the cavity also brought several systematic errors to our attentions. For example, I found that large ±200 pm shifts in tune-out wavelengths can occur due to the Earth's rotation rate. To solve this problem, I demonstrated that controlling the optical polarization, the magnetic field, and the atom beam velocity distribution can either suppress or enhance these systematic shifts. Suppressing these systemic shifts in tune-out wavelengths is useful for precision measurements used to test atomic structure calculations. By enhancing these systematic shifts, the interferometer can be a gyroscope that utilizes tune-out wavelengths.
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Holleczek, Annemarie. "Linear optics quantum computing with single photons from an atom-cavity system." Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:d655fa1c-3405-413d-8af8-eecf6212ab74.
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One of today’s challenges to realise computing based on quantum mechanics is to reliably and scalably encode information in quantum systems. Here, we present a photon source to on-demand deliver photonic quantum bits of information based on a strongly coupled atom-cavity system. The source operates intermittently for periods of up to 100 μs, with a single-photon repetition rate of 1 MHz, and an intra-cavity production efficiency of up to 85%. Our ability to arbitrarily control the photons’ wavepackets and phase profiles, together with long coherence times of 500 ns, allows to store time-bin encoded quantum information within a single photon. To do so, the spatio-temporal envelope of a single photon is sub-divided in d time bins which allows for the delivery of arbitrary qu-d-its. This is done with a fidelity of > 95% for qubits, and 94% for qutrits verified using a newly developed time-resolved quantum-homodyne measurement technique. Additionally, we combine two separate fields of quantum physics by using our deterministic single-photon source to seed linear optics quantum computing (LOQC) circuits. As a step towards quantum networking, it is shown that this photon source can be combined with quantum gates, namely a chip-integrated beam splitter, a controlled-NOT (CNOT) gate as well as a CNOT4 gate. We use this CNOT4 gate to entangle photons deterministically emitted from our source and observe non-classical correlations between events separated by periods exceeding the travel time across the chip by three orders of magnitude. Additionally, we use time-bin encoded qubits to systematically study the de- and re-phasing of quantum states as well as the the effects of time-varying internal phases in photonic quantum circuits.
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Rubenstein, Richard Alan 1971. "Longitudinal atom optics : measuring the density matrix of a matter wave beam." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85255.
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Hu, Zhen Kimble H. Jeff Kimble H. Jeff. "Quantum optics with cold atoms--nonlinear spectroscopy and road toward single-atom trap /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10112007-092812.
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Widerström, Michel. "Entangled photon triplets produced by a third order SPDC process." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64640.
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This thesis describes the work performed at the Quantum Optics lab at UNAM,Mexico City. Third order spontaneous parametric down conversion (TOSPDC) isa quantum optical process where an incoming photon is annihilated and generatesthree quantum entangled photons, so called photon triplets, under energy and mo-mentum conservation. This TOSPDC process was experimentally realized using afused silica optical fiber as nonlinear source. The spectra of the emitted signal weremeasured and coincidence counts measurements were performed in order to verifythe generation of these triplets. An average of 0.8 triplets per second were detected,which is the first sign of a realized TOSPDC process to our knowledge. At thispoint, the signal was too low for any spectra to be recorded. There is a lot of roomfor improvements, especially regarding the equipment used due to the heavy signalloss throughout the experimental setup, and more experiments will be performed toproperly verify the production and entanglement of the triplet photons.
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Barton, Paul Anthony. "Retro-reflection of cold rubidium atoms from a curved magnetic mirror." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266552.
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O'Dell, Duncan H. J. "The diffraction of atoms by light." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265325.
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Fritioff, Tomas. "Precision Improvements of Penning Trap Mass Measurements Using Highly Charged Ions : Applications to solving current problems in fundamental physics." Doctoral thesis, Stockholms universitet, Fysikum, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-616.
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In my thesis I describe the improvements of the Penning trap mass spectrometer SMILETRAP. The objective of these improvements have been to increase the reliability and the accuracy with which an atomic mass can be measured using highly charged ions. The improvements have been achieved by stabilizing both the electric and magnetic fields of the trap and by improving the technical performance of the trap system. As a result it has been possible to measure accurately the mass of several atoms ranging from hydrogen to mercury using charge states from 1+ to 52+. It was only possible to use the highest charge states after applying a successful cooling of these ions with Helium during the charge breeding. The technical improvements made a number of interesting accurate mass measurements possible. The measurements of the 3H, 3He, and 4He masses showed that the previously values were wrong. The mass difference between 3H and 3He which is the Q-value of the tritium beta decay has been determined to 18.588(3) keV. The Q-value of the double β-decay of 76Ge was measured at an accuracy of 50 eV. This value is indispensable for the evaluation the Heidelberg-Moscow experiment which aims at finding a possible neutrino-less decay which if present would be a violation of the standard model. The mass ratio of mCs/mp is used to determine the fine structure constant independent of QED calculations. The two decades old anomaly in the mass values of Hg was solved by the mass determination of 198Hg and 204Hg. The mass of 24Mg was measured at an uncertatinty of 0.6 ppb and will be used in the determination of the g-factor of a bound electron in a hydrogen like ions.
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Eriksson, Mirjam. "Tunable diode laser absorptionspectroscopy of atomic potassium in a KOH-seeded flat flame." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-146503.
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Potassium (K) is the main ash-forming element released from biomass during thermochemical conversion. A better understanding of K chemistry and monitoring of K species is needed to optimize combustion systems. Since K species are highly reactive and prevailing concentrations depend on the conversion conditions, accurate quantification requires in situ measurement techniques. Tunable diode laser absorption spectroscopy with a single-mode distributed feedback laser is used to probe the D1 transition of atomic potassium, K(g), at 769.9 nm. The large current tuning range of the diode laser (5 cm-1) enables monitoringthe wings of the absorption profile. Fitting to the acquired line shape wings is used as astrategy to enhance the dynamic range of the sensor and measure K(g) concentrations even under optically thick condition. A potassium-rich combustion environment is simulated by converting KOH salt in a premixed methane/air flat flame. Quantitative measurements of K(g) are made at 75 positions in the flame. This yields radial K(g) profiles at three different heightsin the plume above the KOH salt and an axial profile at the burner center. The acquired average K(g) concentrations are corrected for effective plume size, i.e. the absorption pathlength determined from the radial profiles. Knowledge of the K(g) distribution in flames can lead to a better understanding of K release and primary reaction kinetics.
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Hjältén, Adrian. "Modeling the cavity dispersion in cavity-enhanced optical frequency comb Fourier transform spectroscopy." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-157146.
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Cavity enhanced optical frequency comb spectroscopy is a technique that allows for quick and sensitive measurements of molecular absorption spectra. Locking the comb lines of an optical frequency comb to the cavity modes of an enhancement cavity and then extracting the spectral information with a Fourier transform spectrometer grants easy access to wide segments of absorption spectra. One of the main obstacles complicating the analysis of the measurements is the inevitable dispersion occurring inside the cavity. In this project, absorption measurements of CO2 were performed using an existing and well established setup consisting of a near-infrared optical frequency comb locked to a Fabry- Pérot enhancement cavity using the Pound-Drever-Hall technique, and a Fourier transform spectrometer. The purpose was to improve theoretical models of the measured absorption spectra by creating and verifying a model for the cavity dispersion, stemming mostly from the cavity mirrors but also from the normal dispersion of the intracavity medium. Until now, the cavity dispersion has been treated as an unknown and was included as a fitting parameter together with the CO2 concentration when applying fits to the absorption measurements. The dispersion model was based on previously performed precise measurements of the positions of the cavity modes. The model was found to agree well with measurements. In addition, pre-calculating the dispersion drastically reduced computation time and seemed to improve the overall robustness of the fitting routine. A complicating factor was found to be small discrepancies between the locking frequencies as determined prior to the measurements and the values yielding optimum agreement with the model. These apparent shifts of the locking points were found to have a systematic dependence on the distance between the locking points. The exact cause of this was not determined but the results indicate that with the locking points separated by more than about 10nm the shifts are negligible.
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Mastrothanasis, Helene Alexandra. "Simultaneous measurement and discrimination of temperature and strain in distributed fiber optical systems with fiber Bragg gratings." Thesis, Uppsala universitet, Fasta tillståndets fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-454878.
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This master thesis deals with simultaneous measurement and discrimination of temperature and strain using fiber Bragg gratings(FBGs). Saab Avionics is seeking for a further development of the overheat detection system that gives a warning when a heat leakage is detected. A further development is to distinguish between temperature and strain and give a warning when strain occurs that correspond to a temperature increase of 10°C. The present work was performed for Saab Avionics and the experiments were carried out in Kungliga Tekniska Högskola(KTH) at department of Laser Physics. The aim of this thesis was to study some methods for simultaneous measurement of temperature and strain with FBGs and try to discriminate them. Two methods were investigated, a sensor design containing a boron-codoped germanosilicate fiber and a germanosilicate fiber and fibers with different cladding diameters. The gratings were heated in an oven and stressed with solder between a translation stage and a stationary stage. For the boron-codoped germanosilicate fiber the temperature sensitivity was ~ 2 times lower than the germanosilicate fiber, while they had similar strain responses. For the second sensor design with different cladding diameters, for a 80 μm cladding diameter the strain response was ~ 2.5 times higher that the 125 μm cladding diameter, while for a 100 μm cladding diameter the strain response is ~ 1.6 times higher than the 125 μm cladding diameter. For a 125 μm, a 100 μm and a 80 μm cladding diameter the temperature sensitivities were similar.
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Zachmann, Nils. "Characterisation of a Gas Modulation Refractometer for Detection of Gases at 1550 nm." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-148557.
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Only very few molar polarizabilities are known with high accuracy; and when so, they are in general only known at a given wavelength. There is therefore a need to assess the molar polarizability with high accuracy of various gases, at different wavelengths. The molar polarizability of a gas is a measure of the susceptibility of a molecule to have its charge distribution affected by light. It is also the entity that relates the index of refraction to the (molar) density of a gas in Lorentz-Lorenz equation. Hence, for high precision measurements of the density of a gas, it is important to know the molar polarizability of the gas to high accuracy. In this work a GAMOR system has been used to determine the wavelength-dependent molar polarizability of Ar at 1550 nm. However, a high accuracy assessment of the molar polarizability of a gas requires that the gas density is known with high accuracy. Since this is not trivial to assess, the molar polarizability of argon has been assessed in terms of that of nitrogen, which is assumed to be known with high accuracy. Hence, to minimise measurement errors, the measurement cavity was alternately filled with nitrogen and argon and the ratio between the signals provided by the GAMOR system represents the ratio of the molar polarizabilities of the two gases. It was found that the molar polarizability of argon was 0.94393(5) times that of nitrogen. Since the latter one has been assessed to 4.34828(3) x 10^-6 m^/mol, the molar polarizability of argon could be assessed to 4.10446(5) x 10^-6 m^3/mol.
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Moretti, Francesco. "A Model Investigation of Photoionization Delay for Atomic Clusters." Thesis, Stockholms universitet, Fysikum, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-159523.
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Nagy, Gergely. "Observation, control, and automation of an OPCPA system." Thesis, Umeå universitet, Institutionen för fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-180702.
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Vantaraki, Christina. "Investigations of coherent and incoherent diffractive imaging." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-411840.
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Erbing, Axel. "In pursuit of next generation photovoltaics : An electronic structure study of lead-free perovskite solar cells." Licentiate thesis, Stockholms universitet, Fysikum, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-181608.
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The recent development of perovskite-based solar cells have shown a remarkably fast increase in power conversion efficiency making them a promising low-cost alternative to conventional cells. The most successful class of materials however, the lead-halide perovskites, are held back due to toxicity and stability issues significantly limiting their use. Because of this, the investigation of new, lead-free, light-absorber materials as a replacement is an important step towards improved solar cells. The focus of this licentiate thesis is the study of bismuth-based materials and their photovoltaic properties through electronic structure calculations. Specifically, the cubic-phase AgBi2I7 under gradual substitution of either bromine or antimony is investigated using density functional theory under periodic boundary conditions. This enables calculations of the system's energy levels and band structure. Furthermore, the energy variance of the employed model of the system is sampled with respect to its level of ion disorder to obtain a better understanding of the distribution of ions within the crystal. The materials are found to have good optical properties but comparatively low efficiencies. The introduced substitutions allow fine-tuning of the system's band gap and is shown to increase the overall performance of the solar cells. In addition, spin-orbit coupling effects are demonstrated to be important when treating these bismuth-based systems. The crystal structure is found to have a significant preference for separating its silver ions and cation vacancies.
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Mommers, Cornelis Johannes Gerardus. "Universal Quantum Computation Using Discrete Holonomies." Thesis, Uppsala universitet, Materialteori, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444209.
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Luani, Giacomo. "Optimization of e-beam and x-ray target geometry of a solid x-ray anode source." Thesis, Uppsala universitet, Materialfysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446042.
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The X-ray tube is one of the most common types of X-ray sources, which is widely used in research laboratories and industry. Electrons are accelerated towards a metallic target to generate X-ray photons, thus creating a significant thermal load on the metal. In order to reduce the risk of damage, some techniques, such as the focus line principle or the installation of a very thin target, are implemented in most cases. In addition, the geometry of the target is chosen to maximise the amount of X-rays for the intended application. The aim of this thesis is to investigate how the incident angle of the electron beam, consequence of the line focus principle, and the thickness of the target influence the total photon yield of the source. Monte Carlo simulations of electron/photon transport have been made with a modified version of the PENELOPE program using a novel variance reduction technique. The results from the calculations are validated with experiments conducted with a prototype source, in the laboratory of Excillum AB. Since thermal capabilities and X-ray yield have opposite dependence on target angle and thickness, by combining the thermal results from Sara Högnad$\acute{\mathrm{o}}$ttir's thesis and the ones produced in this thesis, it is possible to isolate an optimal configuration of the source. In this geometry, the best compromise between high brightness and high maximum allowed power is found.
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Bijedic, Adi. "Sustaining Orientation of Ubiquitin for Single Particle Imaging Using Electric Fields." Thesis, Uppsala universitet, Kemisk och biomolekylär fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-443586.
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Single-particle imaging, or SPI, is a method used to obtain the three-dimensional structure of particles. Repeatedly aiming X-rays at samples of a particle produces diffraction patterns, which are combined to a best-fit three-dimensional model of the particle. SPI of proteins can be improved by orienting the protein before imaging. Protein dipole orientation makes use of a protein's dipole moment and an external electric field to generate torque, which can orient the protein. A protein subject to an electric field may however result in damage of the protein's geometrical structure, or insufficient protein orientation, depending on the magnitude of the electric field. Sufficient protein orientation without substantial protein damage is possible in an interval of electric field strengths. The results in this report reveal that the method of SPI can be further improved. With a protein being fully oriented in an electric field, it is possible to reduce the electric field strength and yet sustain sufficient orientation, with some constraints. Longer times for imaging and less structural damage to the protein are hence possible. This study implements Molecular Dynamics (MD) and the most extensively used open-source MD software, GROMACS, with ubiquitin as a sample protein.Single-particle imaging, eller SPI, är en metod som används för att erhålla den tredimensionella strukturen hos partiklar. Genom att upprepade gånger rikta röntgenstrålar mot prover av en partikel produceras diffraktionsmönster, som kombineras till en anpassad tredimensionell modell av partikeln. SPI av proteiner kan förbättras genom att i förväg rikta proteinet. I dipolorientering av ett protein utnyttjas proteinets dipolmoment och ett yttre elektriskt fält för att generera vridmoment, vilket kan rikta proteinet. Ett protein som utsätts för ett yttre elektriskt fält kan dock resultera i att proteinets geometriska struktur skadas, eller att proteinets riktning avviker avsevärt, beroende på magnituden av det elektriska fältet. Det är möjligt att rikta ett protein inom ett intervall av elektrisk fältstyrka utan att proteinet skadas avsevärt. Resultaten i denna rapport avslöjar att metoden för SPI kan förbättras ytterligare. Med ett protein som i förväg riktats i ett elektriskt fält är det möjligt att sänka fältstryrkan och ändå upprätthålla riktningen, med vissa begränsningar. Längre tid för avbildning och mindre omfattande strukturella skador möjliggörs med detta. Denna studie implementerar Molecular Dynamics (MD) och den mest använda programvaran med öppen källkod för MD-simuleringar, GROMACS, med proteinet ubiquitin som prov.
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Fakhri, Maryam. "Near-infrared optical frequency comb Vernier spectroscopy in air and in a flame." Thesis, Umeå universitet, Institutionen för fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-132520.
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A Vernier spectrometer is built with a near-infrared mode-locked Er:doped fiber laser, a Fabry-Perot cavity with finesse of 1000, a diffraction grating and a photo detector. The optical cavity provides high sensitivity in absorption detection by enhancing the interaction length of the light with molecular species contained in the cavity. Coupling an optical frequency comb to the cavity provided a broadband spectral bandwidth with high precision to measure the absorption of several molecular species simultaneously. Also, by using the optical cavity as a filter, transmission of some bunch comb lines was achieved. This comb filtering together with a simple grating and a photodiode formed the Vernier detection technique to provide very fast measurements while it kept the setup very simple and compact. The system allows to detect carbon dioxide in the air and water vapor and OH radicals in the flame in a spectrum spanning from 1550 nm to 1590 nm, approximately. The retrieved spectrum has a resolution of 9.3 GHz being acquired in 0.05 s.
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Umair, Muhammad. "Resonances in three-body systems." Licentiate thesis, Stockholms universitet, Fysikum, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-109120.
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Three particles interacting via Coulomb forces represents a fundamental problem in quantum mechanics whose approximate solution provides some insight into the more complex analysis associated with few-body problems. We have investigated resonance states composed of three particles interacting via Coulombic and more general potentials in non-relativistic quantum mechanics, using the complex scaling method. My calculations have been applied to two different physical systems: (i) an investigation of the possibility of resonances in the $p e \mu$ system, which has been suggested as a possible reason for unexpected results from a recent measurement of the proton radius in muonic hydrogen (ii) a calculation of resonances in positron-hydrogen scattering, which shows that we can represent this system with the accuracy needed for future scattering calculations. The basis set used is built from Gaussians in Jacobi coordinates, thus automatically including mass-polarisation effects which cannot be neglected in muonic systems.
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Thorin, Emil. "Towards the carrier-envelope phase stabilization of a16 TW 4.5 fs laser system." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-152443.
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In the last decades the scientific development has made it possible to produce pulses with durations below the femtosecond time scale (1 fs = 1015 s), reaching to attoseconds (1 as = 1018 s). This is the time scale of electronic motion inside atoms and molecules. One way to produce isolated attosecond pulses is through high harmonic generation in gases with intense few-cycle laser pulses. This process depends strongly on the electric field shape relative to the pulse envelope, which is characterized by the so called carrier-envelope phase (CEP).The goal of this master’s thesis is to measure and investigate the possibility to improve the CEP stability of sub-two-cycle laser pulses from the laser, Light Wave Synthesizer 20 (LWS-20). The first step of the master’s thesis was to modify a Labview program used to evaluate the CEP change to be able to reevaluate the already acquired raw data. The measurements are done with an f-to-2f interferometer, whichis a spectral interference device, which measures the CEP difference between two pulses. The CEP change of the laser system was measured at three positions: after the multi-pass amplifier of the laser front end (MP), after a hollow-core fiber (HCF), which is used for spectral broadening, and at the end of the laser system. The stability is determined as the RMS error (standard deviation) of the phase change overall shots in one sample (lower RMS is better stability). The measurements show an average stability of 160±20 mrad RMS after the MP, 280±31 mrad RMS after the HCF and 560±53 mrad RMS at the end of the system. The stability at the end of the system could be improved to 475±40 mrad RMS after a scan of the pump energy for one of the amplifier stages. The HCF appears to provide a lower limit in stability and influences it only if it is very good after the MP. The alignment of the HCF does also seem to influence the CEP stability and the best stability appears to coincide with maximum output energy. An acousto-optic modulator (Dazzler) has been used to manipulate the CEP change at the end of the system and can thereby compensate for long-term drifts, but the source of the CEP stability degradation at the end of the system should be further investigated.
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Öström, Jonatan. "Development of a water model with arbitrary rank multipolar polarization, repulsion and electrostatics." Licentiate thesis, Stockholms universitet, Fysikum, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-167840.
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I report on the derivation, development and computer implementation of methods for computing the energies and forces between small rigid polarizable molecules, that are defined by the center-of-mass moments of their electronic and nuclear charge distributions and their linear response moments. The formalism is based on compact and efficient storage and manipulation of symmetric Cartesian tensors of arbitrary rank, and a general formula for the Cartesian gradients of one-dimensional interaction (kernel) potentials. The theory is applied to many-body interactions among water molecules. Permanent moments of the water molecule are computed up to the 9th order with quantum-chemistry software and their basis-set dependence is investigated. Response moments up to the 5th order are similarly investigated. Kernel potentials for electronic, nuclear and polarized interactions are suggested and compared to interaction energies from symmetry-adapted perturbation-theory. I discuss vibrational degrees of freedom and report on a novel method for fitting high rank moment tensors to a flexible geometry. The method is based on decomposition of the tensor into a sum of outer products of vectors, which are defined in the lab-frame by the molecular geometry. I show that the formalism, which is based on an asymptotic expansion, can give good results at all ranges.
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Eriksson, Ronja. "Evaluation of properties of a digital micromirror device applied for light shaping." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74521.
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Kiselman, Klara. "Studies of Molecular Carbon Cluster Dianions in DESIREE." Thesis, Atomic Physics division, Department of Physics, Stockholm University, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387327.
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Since the surprising first detection of small carbon cluster dianions by Compton et al 1990, several studies have been made investigating their structure, fragmentation pathways and stability. As other carbon anions have been found in space, it is likely that these dianions exists as well and their ability to react with other molecules is therefore of interest. Previous studies have shown that they may survive on microsecond timescales, but it is still an open question whether they are metastable or thermodynamically stable. Therefore, this study utilizes the cyrogenic storage ring DESIREE to investigate the lifetime and stability of carbon cluster dianions Cn(2-) (n=7-10) in the new domains. Dianions were produced with a cesium ion sputtering source and their spontaneous decay Cn(2-) -> Cn(-) + e- was monitored for almost 100 ms by detection of the singly charged decay products. Also, the extra electron's tunneling probability through the repulsive coloumb barrier for C8(2-) was calculated and the lifetime for different energy states was estimated. Analyzing the DESIREE data, the lifetime of the dianions could be determined to exceed the previous concluded lifetimes of 10 us by a whole order of magnitude. The only way to detect stable ions after that would be if they collided with rest gas and due to good vacuum, this eventual signal is too low. Probably due to varying structures, an alternating pattern was found, dianions with even n decaying slower than their odd neighbours. The fitting of power laws to the data is consistent with that the dianions were produced with a broad internal energy distribution. Calculations for C8(2-) indicated that its electron affinity had to be at least -1eV in order to agree with the experimental results. Continuing the investigations, future studies could, after sufficient time, use DESIREE in an alternative way, allowing detection of possible stable dianions.
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VANTARAKI, CHRISTINA. "Counteraction of urea-induced protein denaturation by Trimethylamine N-oxide." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-390487.
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A common consequence of protein denaturation is the loss of biological activity. Natural osmolytes such as Trimethylamine N-oxide (TMAO) contribute to protein folding, whereas other osmolytes such as urea act as an agent in the denaturation of proteins. Many studies have shown that denaturation of proteins could occur for certain concentrations of urea, however, this effect could be prevented with the presence of Trimethylamine N-oxide (TMAO) molecules. The aim of the present study is to find out the mechanism of TMAO as a protein stabilizer against urea. Firstly, Molecular Dynamics simulations were carried out for 1, 8, 27 and 64 TMAO molecules. The time-average location of the TMAO molecules during the simulation was studied by the partial density. These simulations examine if TMAO is amphiphilic molecule, i.e contains both hydrophobic and hydrophilic parts. However, these results might not be representative due to bad statistics. Secondly, an experiment ran at BESSY II at Helmholtz-Zentrum Berlin using X-ray Photoelectron Spectroscopy in liquids. In this experiment, Lauryldimethylamine oxide(LDAO) was used instead of Trimethylamine N-oxide (TMAO) due to some practical reasons. The behaviour of urea and LDAO molecule was studied when these molecules were in different and same solutions. The purpose of this experiment is to find out the mechanism of LDAO against urea. Finally, LDAO interacts with urea and a possible mechanism between them is suggested. A common consequence of protein denaturation is the loss of biological activity. Natural osmolytes such as Trimethylamine N-oxide (TMAO) contribute to protein folding, whereas other osmolytes such as urea act as an agent in the denaturation of proteins. Many studies have shown that denaturation of proteins could occur for certain concentrations of urea, however, this effect could be prevented with the presence of the Trimethylamine N-oxide (TMAO) molecules. The aim of the present study is to find out the mechanism of TMAO as a protein stabilizer against urea. Firstly, Molecular Dynamics simulations were carried out for 1, 8, 27 and 64 TMAO molecules. The time-average location of TMAO molecules during the simulation was studied by the partial density. These simulations examine if TMAO is amphiphilic molecule, i.e contains both hydrophobic and hydrophilic parts. However, these results might not be representative due to bad statistics. Secondly, an experiment ran at BESSY II at Helmholtz-Zentrum Berlin using X-ray Photoelectron Spectroscopy in liquids. In this experiment, Lauryldimethylamine oxide (LDAO) was used instead of Trimethylamine N-oxide (TMAO) due to some practical reasons. The behaviour of urea and LDAO molecule was studied when these molecules were in different and same solutions. The purpose of this experiment is to find out the mechanism of LDAO against urea. Finally, LDAO interacts with urea and a possible mechanism between them is suggested.
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Andersson, Kent. "Preparation and Characterisation of Sputtered Titanium- and Zirconium Nitride Optical Films." Licentiate thesis, Solid State Physics Group, Department of Technology, Uppsala University, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-4530.
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Multilayered interference coatings based on titanium- and zirconium nitride and designed for solar control have been prepared using reactive d c magnetron sputtering. Preparation effects and degradation mechanisms were investigated. It was shown that the quality of the nitride strongly depends on the degree of crystallinity in the underlying oxide. It has been shown that the nitride layer partly oxidizes as the top oxide layer is deposited. The degradation is enhanced with temperature. A thin sacrificial layer of aluminium deposited between successive depositions of nitride and oxide is shown to improve the optical performance of the coating as preparedm as well as after accelerated ageing tests. The optical properties of opaque and semitransparent films of zirconium nitride have been studied. A thorough investigation of the influence of composition, deposition rate, substrate temperature and film thickness on the optical response of the film was performed. Both photometric and ellipsometric methods were used to determine thicknesses and the optical constants at wavelengths ranging from 0.23 to 25 μm. The resulting values of n and k, in the wavelength intervals where these independent methods are applicable, have been shown to agree extremely well. The results so far indicate an even larger potential for zirconium nitride based solar control coatings as compared to the titanium nitride based. Access to optical constants derived from films of zirconium nitride of variable quality made multilayer modelling a powerful tool in the design and analysis of solar control coatings.
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Wu, Xiuyu. "Generation and characterization of intense attosecond XUV pulses." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165564.
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Electronic dynamics in molecules and atoms takes place on the attosecond timescale. For the observation of such processes, measurement techniques with attosecond resolution are needed. High-harmonic generation (HHG) in gas medium provides an ultrashort light source on the attosecond timescale for observing, understanding and controlling light-induced process on this scale with the necessary time resolution. To be able to use these attosecond pulses to measure electron dynamics, they have to be characterized. For this characterization, the XUV spectrum is extremely important. The XUV spectrum not only contains the information about the photon energies of the pulses, but also temporal information such as the difference between a single isolated attosecond pulse or an attosecond pulse train. The Light Wave Synthesizer 20 generates intense femtosecond pulses with a peak power of 16 TW and a spectrum spanning over the region from 580 to 1000 nm. This allow one to generate attosecond pulses based on HHG in gas medium with 100 eV photon energy and up to 20 nJ pulse energy. The generated attosecond pulses can be observed with a photodiode to measure the energy, an XUV CCD used as a profiler and an XUV flat-field spectrometer. The detector of the flat-field spectrometer is an XUV CCD which records the diffracted beam from a grating. Hence, a certain pixel of the camera shows the intensity for a certain range of photon energies. However, the calibration from pixel to energy is not always fixed due to e.g. the alignment of the spectrometer. This pixel to photon energy calibration can be done either by using the harmonic peaks in the XUV spectra or theoretical analyses of the spectrometer structure. In this thesis, both methods are investigated and the results are in good agreement. Due to the analytical calibration has a lower error and faster to do, future measurements can be evaluated with the analytical method.
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Zhang, Xiaoying. "Contrast improvement of few-cycle pulses." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165565.
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The intense few-cycle laser pulses play an important role in the investigations of laser-plasma interaction. However, one of the biggest challenges in their generation is the reduction of temporal intensity contrast by introducing undesired pre-pulses and a long pedestal. Two techniques were investigated in this work to improve the contrast. First, the crossed-polarized wave (XPW) generation was optimized to get clean pulse. The conditions for XPW were optimized including crystal thickness and maximal background pressure in the vacuum cell. Second, the method of elliptical polarization rotation (EPR) in a gas-filled hollow-core fiber (HCF) was implemented to produce both broadened and cleaned pulse, since its setup is much simpler. For the tested EPR-based nonlinear filter, the spectral smoothening and broadening were obtained. The contrast of cleaned pulse was characterized providing 2 order of magnitude contrast enhancement, while it had a high average power of 80 mW. The EPR-based nonlinear filter is a promising simplified technique in the development of intense few-cycle lasers.
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Wu, Xiuyu. "Optimization of Intense Attosecond XUV Pulses." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165569.
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To observe electron dynamics in molecules and atoms which takes place on the attosecond timescale, single isolated attosecond pulses are required utilized in performing pump–probe experiments. The Light Wave Synthesizer 20 generates intense sub-5 fs pulses with a peak power of 16 TW and a broad spectrum. This offers a chance of generating isolated attosecond pulses via high harmonic generation (HHG) in gas medium. In this project, the variation of cutoff energy of HHG with different intensities of the driving laser was investigated. In addition, an isolated attosecond pulse with an Fourier-limited pulse duration of 188 as is produced with a selection of 15 eV around the cutoff region. Moreover, one optimization method refer to GDD scan was illustrated to optimize the HHG cutoff and continuum.
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Chang, Liu. "Ghost in the shell : Studies on subsurface oxygen in oxide-derived copper nanocube catalysts." Licentiate thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-147215.
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With the passage of time and the advancement of our industrial civilization, environmental concerns have become more and more recognized since the 1990s. Carbon dioxide reduction reactions are capable of converting carbon dioxide into valuable hydrocarbons and reducing the carbon emission from the combustion of fossil fuels. This is a promising direction for sustainable energy resources given that the scarcity of fossil fuels is becoming more threatening to the survival of mankind. In recent years, oxide-derived metal nanostructures have been synthesized and show unique catalytic features. Recently, Sloan et al. synthesized a novel oxide-derived copper nanocube structure, which showed a high selectivity toward ethylene over methane and low overpotentials. In this work, the presence of subsurface oxygen in the catalyst surface is tested with density functional theory (DFT) calculations, as a complement to experimental x-ray photoelectron spectroscopy. Due to limitations on the scale of modeling with DFT, the results indicate a very low stability of subsurface oxygen, which give rise to a question if subsurface oxygen would be stable with a reasonably large cluster model. Self-consistent charge density functional tight binding (SCC-DFTB) is adopted to investigate a nanocube model. In this model, a manually reduced cuprious oxide nanocube is constructed and investigated. Subsurface oxygen atoms close to facets are found to be more stable inside. A higher degree of disorder is proposed to be the cause of this difference in stabilizing subsurface oxygen atoms between the slab and nanocube models. The presence of subsurface oxygen enhances the adsorption of CO on the Cu(100) surface, increasing the likelihood for adsorbed CO molecules to dimerize, which is the rate determining step for ethylene production on Cu(100) under low-overpotential conditions. With subsurface electronegative atoms such as oxygen or fluorine, it is also found that the d-band scaling relation could be broken.